Tuning of polishing process in multi-carrier head per platen polishing station

ABSTRACT

An apparatus and method for simulating a substrate being polished in a multiple carrier head per platen station when no substrate is provided in one or more of the multiple carrier heads is described. In one embodiment, a method for processing a substrate includes providing a single substrate to a polishing station adapted to process a plurality of substrates on a single polishing pad using at least a first carrier head and a second carrier head, retaining the single substrate in the first carrier head while the second carrier head remains substrate-free, urging the first carrier head and the second carrier head toward a polishing surface of the polishing pad; and providing relative movement between the polishing pad and the first carrier head.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to polishing asubstrate, such as a semiconductor substrate. More specifically,embodiments relate to tuning a polishing process on a substrate in amulti-carrier head per platen polishing station.

2. Description of the Related Art

Chemical mechanical polishing (CMP) is one process commonly used in themanufacture of high-density integrated circuits to planarize or polish alayer of material deposited on a substrate. The substrate may beprovided to a polishing station and retained in a carrier head thatcontrollably urges the substrate against a moving polishing pad mountedon a platen. CMP is effectively employed by providing contact between afeature side of the substrate and moving the substrate relative to thepolishing pad while in the presence of a polishing fluid. Material isremoved from the feature side of the substrate that is in contact withthe polishing surface through a combination of chemical and mechanicalactivity.

Conventional CMP polishing stations may contain multiple carrier headsper platen such that multiple substrates may be processed simultaneouslyon a common polishing pad supported by a platen. The conventionalpolishing stations are effective in increasing throughput by polishingmore than one substrate at a time and/or reducing tool footprint. Thesestations are effectively utilized when the number of substrates to bepolished equal the number of carrier heads per platen. Process recipesin these stations are known and factors such as polishing fluidconcentration, polishing fluid distribution, as well as heat generatedby multiple substrates being polished on a single pad are utilized toprovide optimum removal rates and removal profiles. However, there maybe instances when one or more of the carrier heads are not utilized in apolishing process. The non-use of the one or more carrier heads maydetrimentally affect the polishing process on other substrates beingpolished in the used carrier heads.

Therefore, there is a need for a method and apparatus that is utilizedto control polishing parameters on a substrate being polished in acarrier head in a multiple carrier head per platen station other carrierheads do not contain a substrate.

SUMMARY OF THE INVENTION

The present invention generally provides an apparatus and method forsimulating a substrate being polished in one or more carrier heads in amultiple carrier head per platen station when no substrate is present inthe one or more carrier heads. In one embodiment, a method for tuning apolishing process on a substrate in a processing station having at leasta first carrier head and a second carrier head adapted to retain andprocess a substrate using a common polishing pad is described. Themethod includes retaining a single substrate in a first retaining ringdisposed on the first carrier head while the second carrier head remainsempty, urging the first carrier head and the single substrate toward apolishing surface of the polishing pad while bringing the secondretaining ring disposed on the second carrier head into contact with thepolishing surface, the second carrier head remaining empty, providingrelative motion between the single substrate and the polishing pad, andvarying at least one of a pressure of the second retaining ring againstthe polishing pad and a rotational speed of the second retaining ringrelative to the polishing pad.

In another embodiment, a method for tuning a polishing process on atleast a first substrate in a polishing station adapted to process atleast one substrate greater than the first substrate on a commonpolishing pad is described. The method includes retaining the firstsubstrate in a first retaining ring disposed on at least one usedcarrier head, urging the first retaining ring disposed on the at leastone used carrier head and a second retaining ring disposed on at leastone empty carrier head toward a polishing surface of the polishing pad,the at least one empty carrier head remaining substrate-free, andproviding relative movement between the polishing pad and the at leastone used carrier head.

In another embodiment, a method for processing a substrate is described.The method includes receiving at least one substrate in a polishingstation adapted to process a number of substrates greater than the atleast one substrate on a common polishing pad using at least a firstcarrier head and a second carrier head, positioning the at least onesubstrate in a retaining ring disposed on the first carrier head whilethe second carrier head remains empty, urging the first carrier head andthe second carrier head toward a polishing surface of the polishing pad,and providing relative movement between the polishing pad and the firstcarrier head.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a plan view of a polishing module.

FIG. 2 is a partial cross-sectional view of one embodiment of apolishing station of FIG. 1.

FIG. 3 is a graph representing removal rates of substrates retained inone of the carrier heads of the polishing station of FIG. 2.

FIG. 4 is a graph representing removal profiles of substrates retainedin one of the carrier heads of the polishing station of FIG. 2.

FIG. 5 is a graph representing topographical data obtained frompolishing substrates retained in one of the carrier heads of thepolishing station of FIG. 2.

FIG. 6 is a flowchart showing one embodiment of a method of the presentinvention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to polishing asubstrate, such as a semiconductor substrate, utilizing a chemicalmechanical polishing (CMP) process. The CMP process is described in apolishing system having multiple polishing stations. Each of thepolishing stations contain multiple carrier heads operable on a commonplaten to increase throughput and/or reduce tool footprint. A multiplecarrier head per platen station that may benefit from embodiments of theinvention is a REFLEXION GT™ polishing system available from AppliedMaterials, Inc. of Santa Clara, Calif. However, the REFLEXION GT™polishing system is only representative and other polishing systemsand/or polishing stations may benefit as well. The CMP process isexemplarily described utilizing a circular pad disposed on a rotatableplaten. However, other embodiments may be used on polishing pads havingother shapes, such as rectangular polishing pads or belt-type polishingpads.

FIG. 1 is a plan view of a polishing module 100 for processing one ormore substrates. The polishing module 100 includes a polishing platform106 that at least partially supports and houses a plurality of polishingstations 124. Each of the plurality of polishing stations 124 areadapted to polish substrates that are retained in one or more carrierheads 126. The polishing stations 124 may be sized to interface with theone or more carrier heads 126 simultaneously so that polishing of one ormore substrates may occur at a single polishing station 124 at the sametime. The carrier heads 126 are coupled to a carriage 108 that ismounted to an overhead track 128. The platform 106 also includes one ormore load cups 122 adapted to facilitate transfer of a substrate betweenthe carrier heads 126 and a factory interface (not shown) or otherdevice (not shown) by a transfer robot 110. The load cups 122 generallyfacilitate transfer between the robot 110 and each of the carrier heads126.

The overhead track 128 allows each carriage 108 to be selectivelypositioned around the polishing platform 106. The configuration of theoverhead track 128 and carriages 108 facilitates positioning of thecarrier heads 126 selectively over the polishing stations 124 and theload cups 122. In the embodiment depicted in FIG. 1, the overhead track128 has a circular configuration (shown in phantom) which allows thecarriages 108 retaining the carrier heads 126 to be selectively rotatedover and/or clear of the load cups 122 and the polishing stations 124.It is contemplated that the overhead track 128 may have otherconfigurations including elliptical, oval, linear or other suitableorientation.

Each polishing station 124 generally includes a polishing pad 130supported on a platen (not shown in FIG. 1) which rotates the polishingpad 130 during processing. In one embodiment, each polishing station 124can accommodate two carrier heads 126 that are capable of retaining twosubstrates simultaneously. In one embodiment, each polishing station 124includes two conditioning modules 132 and two polishing fluid deliverymodules 134. The conditioning modules 132 are utilized to condition orroughen a polishing surface of the polishing pad 130 while the polishingfluid delivery modules 135 provide a polishing fluid to the polishingpad 130. Additionally, each of the polishing fluid delivery modules 134are positioned to independently provide a predetermined distribution ofpolishing fluid on the polishing pad 130. In one embodiment, thepolishing pad 130 is suitable for at least one of a chemical mechanicalpolishing and/or an electrochemical mechanical polishing process.

FIG. 2 is a partial cross-sectional view of the polishing station 124 ofFIG. 1. The polishing station 124 includes a platen 200 with a polishingpad 130 mounted thereon. The platen 200 is coupled to a shaft 202 and amotor 204 to rotate the platen 200 and the polishing pad 130 about arotational axis. The polishing station 124 includes two carrier heads206A, 206B similar to carrier heads 126 as shown in FIG. 1.

Each of the carrier heads 206A, 206B are coupled to a shaft 208A, 208B,which are coupled to a motor 210 to independently lift or lower therespective carrier head 206A, 206B in the Z direction relative to apolishing surface 212 of the polishing pad 130. Each of the carrierheads 206A, 206B are coupled to a rotary actuator 214 that is adapted toindependently rotate the respective carrier head 206A, 206B about arotational axis relative to the polishing pad 130 and platen 200. Thecarrier heads 206A, 206B may also be adapted to sweep across thepolishing surface 212 of polishing pad 130 in a linear (X or Ydirection) or arcuate (X and Y direction) motion provided by actuators(not shown) disposed between the track 128 and carriages 108. Apolishing fluid supply nozzle 218 is disposed above the polishing pad130 for supplying a polishing fluid 220 onto the polishing pad 130.

The polishing pad 130 may be a polymer material, which may be solelydielectric to facilitate removal of materials from substrates during apolishing process. Alternatively, the polishing pad 130 may be at leastpartially conductive to facilitate electrochemical dissolution ofmaterial from substrates in an electrochemical mechanical polishing(ECMP) process. Suitable polymeric materials that may be used includepolyurethane, polycarbonate, fluoropolymers, PTFE, PTFA, polyphenylenesulfide (PPS), or combinations thereof, and other polishing materialsused in polishing substrate surfaces. In one embodiment, polishing pad130 includes at least a polishing surface made of a polymeric material,such as open-pored or closed-pored polyurethane material typically usedin the fabrication of polishing pads for service in the polishing ofsemiconductor substrates. In another application, the polishing pad 130may contain fixed abrasives. Thus, the polishing fluid 220 may be aslurry or an electrolytic fluid depending on the polishing process used.

Each of the carrier heads 206A, 206B include a body 222 circumscribed bya retaining ring 224. Each of the carrier heads 206A, 206B also containa bladder 228 that is adjacent a flexible membrane 230 which contacts abackside of the substrates 216A, 216B as the substrates 216A, 216B areretained in the carrier heads 206A, 206B. The bladder 228 may bepressurized to apply force to the flexible membrane 230 which maydistort the flexible membrane 230. The bladder 228 may be divided intotwo or more variable pressure zones adapted to be pressurizedindividually. In one embodiment, the bladder 228 is divided into fiveseparate pressurizable zones adapted to contain different pressures thatmay be applied to the substrate through the flexible membrane 230.Forces applied to the flexible membrane 230 from the bladder 228 aretransmitted to portions of the substrates 216A, 216B and may be used tourge portions of the substrates 216A, 216B toward the polishing surface212. Additionally, vacuum ports (not shown) may be provided in thecarrier heads 206A, 206B to apply suction to the backside of thesubstrates 216A, 216B facilitating retention of the substrates 216A,216B in the carrier head.

Each retaining ring 224 may contain a material which is chemically inertin a CMP process, such as a plastic, e.g., polyphenylene sulfide (PPS),polyetheretherketone (PEEK), a carbon containing PEEK material, aTEFLON® containing PEEK material, or a composite material. Eachretaining ring 224 is in fluid communication with a variable pressuresource 226. The variable pressure source 226 allows the retaining ring224 to move relative to the body 222 of the respective carrier head206A, 206B in at least the Z direction. The variable pressure source 226is adapted to provide the Z directional movement of the retaining ring224 independent of movement provided by the motor 210. The variablepressure source 224 may provide movement of the retaining ring 224 byapplying negative pressure or positive pressure to the retaining ring224. In one aspect, negative pressure is applied to the retaining ring224 to space the retaining ring 224 away from the polishing surface 212.In another embodiment, the variable pressure source 226 applies apressure of about 1 pound per square inch (PSI) to about 12 PSI to urgethe retaining ring 224 in the Z direction toward the polishing surface212. Examples of carrier heads that may be utilized include the TITANHEAD™ carrier head and the TITAN PROFILER™ carrier head, both availablefrom Applied Materials, Inc. of Santa Clara, Calif.

When an even number of substrates, such as two semiconductor substrates216A, 216B, are provided to the load cups 122 of the polishing module100 (FIG. 1), each carrier head 206A, 206B is positioned over the loadcups 122 to facilitate transfer of the two substrates 216A, 216B fromthe load cups 122 to the carrier heads 206A, 206B. Each carrier head206A, 206B is adapted to hold the substrates 216A, 216B by vacuumapplied by the carrier heads 206A, 206B acting on the backside of thesubstrates and/or pressure applied to the retaining rings 224 from thevariable pressure source 226. Once the substrates 216A, 216B areretained in the carrier heads 206A, 206B, the carrier heads 206A, 206Bare positioned over the polishing pad 130 by action of the carriages 108(FIG. 1) and motors 210 (FIG. 2). Each carrier head 206A, 206B is urgedtoward the processing surface 212 of the polishing pad 130 duringprocessing by forces provided by one or a combination of the motors 210and movement of the retaining ring 224 by pressure from the variablepressure source 226.

The substrates 216A, 216B are held in the retaining rings 224 in amanner that facilitates contact between the feature side of thesubstrate and the polishing surface 212 of the polishing pad 130. Thevariable pressure source 226 provides a pressure of about 6 PSI to about8 PSI to urge the substrate toward the polishing surface 212. Processingfactors such as concentration of the polishing fluid 220, distributionof the polishing fluid 220, roughness of the polishing surface 212 aswell as heat generated by two substrates being polished on the polishingpad 130 are optimized to provide an optimum removal rate and removalprofile on the substrates 216A, 216B retained in the carrier heads 206A,206B. However, when only one substrate is present, the temperature andfluid flow produced affect the polishing process.

For example, when there is a mismatch in the number of substrates to bepolished and the number of available carrier heads, only a fraction ofthe carrier heads will be utilized. For example, when there are twoavailable carrier heads and a single substrate, such as substrate 216Aor 216B, is provided to the polishing station 124, only one of thecarrier heads 206A, 206B will be utilized to polish the singlesubstrate. When only one of the carrier heads 206A or 206B are utilizedto polish the single substrate, the processing dynamics are changed andmay detrimentally affect the polishing process on the single substrate.

Various adjustments may be made to the polishing parameters to optimizethe polishing of the single substrate. In one example, the unusedcarrier head 206A or 206B may be actuated to be spaced away from thepolishing surface 212 while the other carrier head is utilized to polishthe single substrate. Adjustments to flow rate of polishing fluid 220,rotational speed and downforce of the carrier head with the singlesubstrate may be made in an attempt to achieve an optimum removal rateand removal profile on the single substrate. However, the adjustmentsmay be based on trial and error and are time consuming and costly. Inanother example, a dummy substrate may be retained in the unused carrierhead. However, chip manufacturers are disinclined to use a dummysubstrate due to particle contamination and/or chemical reactions thatmay occur due to mismatches between film chemistry and the polishingfluid 220.

The inventors have discovered that the unused or empty carrier head 206Aor 206B may be utilized to mimic the polishing of two substrates.Additionally, the unused carrier head may be used as a control knob totune the polishing process on the single substrate. Thus, processingfactors in the polishing of a single substrate may be maintained in amanner that is substantially similar to the processing factors of thepolishing of two substrates. Further, the unused or empty carrier head206A or 206B may be utilized to tune the polishing process on the singlesubstrate. For example, removal rate, removal profile and/or topographyof the single substrate may be controlled by manipulating the emptycarrier head 206A or 206B over the polishing pad 130.

FIG. 3 is a graph 300 representing removal rate data obtained fromsequential polishing of three individual substrates retained in one ofthe carrier heads 206A or 206B while the remaining carrier head wasempty. Data from each of the three substrates retained in the usedcarrier head are represented as lines 305, 310 and 315 showing removalrates in a time period of 30 seconds. Processing parameters utilized inpolishing each of the substrates, such as rotational speeds of theplaten and/or carrier head, downforce, retaining ring pressure,polishing fluid flow rates as well as other processing parameters weremaintained as if both of the carrier heads contained substrates and wereused in a simultaneous polishing process. Each of the lines 305, 310 and315 represent removal rates of respective substrates. The graph 300shows how the empty carrier head may be utilized to vary or tune theremoval rate of each substrate using various pressures applied to theretaining ring 224 of the empty carrier head.

Line 305 shows a copper removal rate of about 4,000 Angstroms (Å) per0.5 minutes when the retaining ring 224 of the empty carrier head wasmaintained at vacuum, which caused the retaining ring 224 to be spacedaway from the polishing surface 212. Line 310 shows a copper removalrate of about 4,500 Å per 0.5 minutes when the retaining ring 224 of theempty carrier head was urged against the polishing surface 212 at apressure of about 5 PSI. Line 315 shows a copper removal rate of about5,000 Å per 0.5 minutes when the retaining ring 224 of the empty carrierhead was urged toward the polishing surface 212 at a pressure of about 7PSI. Thus, variations in pressure applied to the empty carrier head maybe manipulated to tune the removal rate of the single substrate.

FIG. 4 is a graph 400 representing removal profile data obtained fromsequential polishing of two individual substrates retained in one of thecarrier heads 206A or 206B while the remaining carrier head was empty.Processing parameters utilized in polishing each of the substrates, suchas rotational speeds of the platen and/or carrier head, downforce,retaining ring pressure, polishing fluid flow rates as well as otherprocessing parameters were maintained as if both of the carrier headscontained substrates and were used in a simultaneous polishing process.The pressure applied to the retaining ring of the empty carrier head wasabout 2 PSI to about 8 PSI, such as about 3 PSI to about 6 PSI. Datafrom each of the two substrates retained in the used carrier head arerepresented as lines 405 and 410. The graph 400 shows how the emptycarrier head may be utilized to vary or tune the removal profile ofsubstrates using various rotational speeds applied to the empty carrierhead. The varied rotational speeds create varied friction which resultsin changes in temperature of the polishing surface of the polishing padand/or polishing liquid. Additionally, the varied rotational speedsalter the flow of the polishing fluid across the polishing surface ofthe polishing pad. One or a combination of the temperature change andflow dynamics of the polishing fluid change the removal profile of thesingle substrate.

Line 405 shows the removal profile of a first substrate retained in oneof the carrier heads while the rotational speed of the empty carrierhead was about 7 revolutions per minute (RPM). Line 410 shows theremoval profile of a second substrate retained in one of the carrierheads while the rotational speed of the empty carrier head was about 77RPM. Thus, variations in rotational speeds applied to the empty carrierhead may be manipulated to tune the removal profile of the singlesubstrate.

FIG. 5 is a graph 500 representing topographical data obtained frompolishing three individual substrates retained in one of the carrierheads 206A or 206B while the remaining carrier head was empty. Data fromeach of the three substrates retained in the used carrier head arerepresented as bars 505, 510 and 515. Processing parameters utilized inpolishing of each substrate, such as rotational speeds of the platenand/or carrier head, downforce, retaining ring pressure, polishing fluidflow rates as well as other processing parameters were maintained as ifboth of the carrier heads 206A or 206B contained substrates and wereused in a simultaneous polishing process. Each of the bars 505, 510 and515 represent topographical measurements relative to feature density.The graph 500 shows how the empty carrier head 206A or 206B may beutilized to vary or tune the topography of each of the three substratesusing various pressures applied to the retaining ring 224 of the emptycarrier head.

Areas A-H represent various regions of each of the three substrates.Area A represents 100 μm line width/100 μm space or distance betweenfeatures. Area B represents 50 μm line width/1 μm space or distancebetween features. Area C represents 9 μm line width/1 μm space ordistance between features. Areas D, E, F, G and H represent isolatedline widths (e.g., where no features are near the lines). Areas D, E, F,G and H represent 10 μm, 20 μm, 30 μm, 50 μm and 100 μm isolated linewidths, respectively.

Bar 505 shows data at each area where the retaining ring 224 of theempty carrier head was maintained at vacuum, which caused the retainingring 224 to be spaced away from the polishing surface 212. Bar 510 showsdata at each area where the retaining ring 224 of the empty carrier headwas urged against the polishing surface 212 at a pressure of about 3PSI. Bar 515 shows data at each area where the retaining ring 224 of theempty carrier head was urged toward the polishing surface 212 at apressure of about 6 PSI.

Thus, graph 500 shows that pressure applied to the empty carrier headmay be used to alter the topography of the single substrate.Additionally, as features become more dense, the empty carrier head maydramatically affect the topography of the single substrate.

The data shown in FIGS. 3-5 results from a complex set of interactionsthat affect the polishing of the single substrate. Pressure and/orrotational velocity applied to the retaining ring 224 of the emptycarrier head influences temperature of the polishing pad 130, asperitieson the polishing surface 212, as well as polishing fluid and by-productdistribution. In one example, the combined influences result in highertopography on the single substrate as greater pressure is applied to theretaining ring 224 of the empty carrier head.

FIG. 6 is a flowchart showing one embodiment of a method 600 of thepresent invention. At 610, a substrate is provided to a polishingstation having at least a first carrier head and a second carrier headadapted to process a plurality of substrates on a single polishing pad.In one embodiment, the substrate is a single substrate provided to apolishing station containing two carrier heads per polishing pad.

At 620, the single substrate is retained in the first carrier head. Thesecond carrier head remains substrate-free or empty. At 630, the firstand second carrier heads are urged against a processing surface of thesingle polishing pad. At 640, relative motion between the polishing padand the single substrate retained in the first carrier head is provided.

While the method 600 has been described in a polishing station havingtwo carrier heads sharing a common polishing pad, the method may also beutilized on a polishing station containing three or four carrier headsper polishing pad. In one example, the polishing station may containenough carrier heads to retain and polish at least one additionalsubstrate simultaneously on the single polishing pad than is provided tothe station. In one embodiment, the substrate(s) provided to thepolishing station may be referred to as an “n” substrate, where n is aninteger that is less than the number of carrier heads per platen. Inthis embodiment, the number of available carrier heads per platen may bereferred to as “h” carrier heads. For example, two substrates may beprovided to a polishing station having three carrier heads. In thisexample, n equals 2 substrates and h equals 3 carrier heads. In oneembodiment, the unused carrier head(s) in the exemplary polishingstation is referred to as a “h−n” carrier head and the used carrierhead(s) is referred to as an “h+n” carrier head.

In one aspect, the unused carrier head or the h−n carrier head(s) isutilized to tune the polishing process of a single substrate disposed inthe h+n carrier heads. The polishing process on the substrate beingpolished may be altered by varying rotational speeds of the unusedcarrier head or the h−n carrier head(s), varying pressure of the unusedcarrier head or the h−n carrier head(s) against the polishing pad, andcombinations thereof.

In one embodiment, a retaining ring disposed on the used carrier head orh+n carrier head(s) is urged toward the polishing pad at a firstpressure of about 6 PSI to about 8 PSI while a retaining ring disposedon the unused carrier head or the h−n carrier head(s) is urged towardthe polishing pad at a second pressure that is lower than the firstpressure. In one example, the second pressure is about 2 PSI to about 7PSI, such as about 5 PSI. In another embodiment, the first pressure andthe second pressure are substantially equal.

In another embodiment, the used carrier head or h+n carrier head(s) isrotated relative to the rotating polishing pad at a first rotationalspeed and the unused carrier head or the h−n carrier head(s) is rotatedrelative to the rotating polishing pad at a second rotational speed. Inone aspect, the first rotational speed and the second rotational speedare different. For example, the first rotational speed of the usedcarrier head or h+n carrier head(s) is about 77 RPM while the secondrotational speed of the unused carrier head or the h−n carrier head(s)is about 7 RPM to about 15 RPM. In another embodiment, the firstrotational speed of the used carrier head or h+n carrier head(s) and thesecond rotational speed of the unused carrier head or the h−n carrierhead(s) are substantially equal.

Embodiments described herein generally provide an apparatus and methodfor simulating a substrate being polished in a multiple carrier head perplaten station when no substrate is provided in one or more of themultiple carrier heads. The multiple carrier head per platen stationstypically utilize polishing and cleaner recipes on substrates having thesame film thickness, die layout and integration layer. The multiplecarrier head per platen stations work well when the number of substratesprovided to the station equal the number of carrier heads on thestation. In the case where one or more of the multiple carrier heads arenot provided with a substrate, embodiments described herein provide amethod of using unused carrier heads in the multiple carrier head perplaten station to mimic the dynamics of polishing substrates in each ofthe carrier heads. Further, the unused carrier head or heads may be usedto tune the removal rate, removal profile and/or the topography of thesubstrate being polished. The method as described herein may be utilizedin the polishing of metal films, such as copper or tungsten as well asbarrier and dielectric films, such as tetraethyl orthosilicate (TEOS),tantalum nitride (TaN) and carbon doped silicon dioxide films.

In one operational example, a single substrate is provided to thepolishing station 124 of FIG. 2. The single substrate is retained incarrier head 206A while carrier head 206B remains empty. The platen 200is caused to rotate at a rotational velocity of about 70 RPM to about 90RPM, such as about 80 RPM to about 86 RPM, for example about 83 RPM.Concurrently, the carrier head 206A is caused to rotate at about 70 RPMto about 84 RPM, such as about 72 RPM to about 80 RPM, for example about77 RPM. Polishing fluid 220 is flowed from both polishing fluid deliverymodules 135 (FIG. 1) at a flow rate of about 300 milliliters per minute.A pressure of about 0.5 PSI to about 3.5 PSI, such as about 1.5 PSI toabout 2.8 PSI, for example 2.4 PSI is applied to the bladder 228disposed in the carrier head 206A. The bladder 228 applies pressure tothe backside of the substrate and urges regions of the substrate againstthe polishing surface 212. The retaining ring 224 on the carrier head206A is pressurized at a pressure of about 3 PSI to about 10 PSI, suchas about 4 PSI to about 8 PSI, for example about 6 PSI in order toperform a polishing process on the single substrate.

Simultaneously, the empty carrier head 206B is caused to rotate at about70 RPM to about 84 RPM, such as about 72 RPM to about 80 RPM, forexample about 77 RPM. A negative pressure to about 0.0 PSI is applied tothe bladder 228 disposed in the carrier head 206B to prevent theflexible membrane 230 from contacting the polishing surface 212. Theretaining ring 224 on the carrier head 206B is pressurized at a pressureof about 3 PSI to about 10 PSI, such as about 4 PSI to about 8 PSI, forexample about 6 PSI in order to promote contact between the polishingsurface 212 and the retaining ring 224 on the carrier head 206B. Thus,the carrier head 206B is adapted to create or mimic the dynamics of twosubstrates being polished on the common polishing pad 130. In thisexample, the removal rate and/or the removal profile of the singlesubstrate being polished may be substantially equal to the removal ratesand/or the removal profile of two substrates being polished on thecommon polishing pad 130.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for tuning a polishing process on a substrate in a processing station having at least a first carrier head and a second carrier head adapted to retain and process a substrate using a common polishing pad, the method comprising: retaining a single substrate in a first retaining ring disposed on the first carrier head while the second carrier head remains empty; urging the first carrier head and the single substrate toward a polishing surface of the polishing pad while bringing the second retaining ring disposed on the second carrier head into contact with the polishing surface, the second carrier head remaining empty; providing relative motion between the single substrate and the polishing pad; and varying at least one of a pressure of the second retaining ring against the polishing pad and a rotational speed of the second carrier head relative to the polishing pad.
 2. The method of claim 1, further comprising: urging the first retaining ring disposed on the first carrier head toward the polishing surface of the polishing pad at a first pressure.
 3. The method of claim 2, wherein the second retaining ring disposed on the second carrier head is urged toward the polishing surface at a second pressure that is less than the first pressure.
 4. The method of claim 2, wherein the second retaining ring disposed on the second carrier head is urged toward the polishing surface at a second pressure, the first pressure and the second pressure being substantially equal.
 5. The method of claim 1, wherein the first carrier head is rotated at a first velocity relative to the polishing pad and the second carrier head is rotated at a second velocity relative to the polishing pad that is less than the first velocity.
 6. The method of claim 1, wherein the first carrier head is rotated at a first velocity relative to the polishing pad and the second carrier head is rotated at a second velocity relative to the polishing pad that is substantially equal to the first velocity.
 7. The method of claim 1, wherein the first retaining ring is urged toward the polishing surface of the polishing pad at a first pressure and the second retaining ring disposed on the second carrier head is urged toward the polishing surface of the polishing pad at a second pressure.
 8. The method of claim 7, wherein the second pressure is less than the first pressure.
 9. The method of claim 7, wherein the second pressure and the first pressure is substantially equal.
 10. A method for tuning a polishing process on at least a first substrate in a polishing station adapted to process at least one substrate greater than the first substrate on a common polishing pad, the method comprising: retaining the first substrate in a first retaining ring disposed on at least one used carrier head; urging the first retaining ring disposed on the at least one used carrier head and a second retaining ring disposed on at least one empty carrier head toward a polishing surface of the polishing pad, the at least one empty carrier head remaining substrate-free; and providing relative movement between the polishing pad and the at least one used carrier head.
 11. The method of claim 10, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure that is less than the first pressure.
 12. The method of claim 10, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure, the first pressure and the second pressure being substantially equal.
 13. The method of claim 10, further comprising: providing relative motion between the empty carrier head and the polishing pad.
 14. The method of claim 13, wherein the used carrier head is rotated at a first velocity and the empty carrier head is rotated at a second velocity that is less than the first velocity.
 15. The method of claim 13, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure that is less than the first pressure.
 16. The method of claim 13, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure, the first pressure and the second pressure being substantially equal.
 17. A method for processing a substrate, comprising: receiving at least one substrate in a polishing station adapted to process a number of substrates greater than the at least one substrate on a common polishing pad using at least a first carrier head and a second carrier head; positioning the at least one substrate in a retaining ring disposed on the first carrier head while the second carrier head remains empty; urging the first carrier head and the second carrier head toward a polishing surface of the polishing pad; and providing relative movement between the polishing pad and the first carrier head.
 18. The method of claim 17, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure that is less than the first pressure.
 19. The method of claim 17, wherein the first retaining ring is urged toward the polishing pad at a first pressure and the second retaining ring is urged toward the polishing surface at a second pressure, the first pressure and the second pressure being substantially equal.
 20. The method of claim 17, wherein the first carrier head is rotated at a first velocity and the second carrier head is rotated at a second velocity that is less than the first velocity.
 21. The method of claim 17, wherein the first carrier head is rotated at a first velocity and the second carrier head is rotated at a second velocity that is substantially equal to the first velocity. 